Swash plate tilting angle detector for a swash plate plunger type hydraulic unit

ABSTRACT

A swash plate plunger type hydraulic motor is constituted such that plungers are slidably disposed in respective plunger holes of a motor cylinder, and a motor rolling member having a motor swash plate member is supported in a motor casing in such a manner that it can tilt and roll. A swash plate tilting angle detector for detecting the angle of a swash plate includes an angle detector mounted to a transmission housing and a rotation connection mechanism for connecting the motor rolling member to the angle detector. The rotation connection mechanism includes a first connection rod which is connected to the motor rolling member coaxially to its tilting and rolling axis, a second connection rod connected to the angle detector, and a movable or universal joint for connecting the first connection rod to the second connection rod. The described motor provides a swash plate tilting angle detector which has a high degree of freedom of installation position and permits the displacement of the center position thereof without affecting detection accuracy.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present invention claims priority under 35 USC 119 based onJapanese patent application No. 2003-096868, filed Mar. 31, 2003.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a swash plate tilting angledetector. More particularly, the present invention relates to a swashplate tilting angle detector for detecting the tilting and rolling angleof a swash plate in a swash plate plunger type hydraulic unit such as aswash plate plunger pump or swash plate plunger motor.

[0004] 2. Description of the Background Art

[0005] Until recently, various types of hydraulic continuously variabletransmissions each comprising a combination of a hydraulic pump and ahydraulic motor have been known and implemented. For example, hydrauliccontinuously variable transmissions disclosed in JP-A 6-2753 and JP-B7-88884 are proposed by the applicant of the present application. Eachof the hydraulic continuously variable transmissions disclosed by thesepatent documents comprises a swash plate plunger pump, a swash plateplunger motor and a hydraulic closing circuit for connecting the outletport and inlet port of the swash plate plunger pump to the inlet portand outlet port of the swash plate plunger motor, respectively, whereina pump swash plate member is driven by an engine, a pump cylinder and amotor cylinder are connected to each other above the output shaft of theengine, the rotation of a motor swash plate member is restricted, andthe angle of a motor swash plate can be changed.

[0006] In this hydraulic continuously variable transmission, a pumpcylinder and a motor cylinder are connected to each other back to back,and pump and motor distributor valves (distributor valves) are arrangedin this connection portion to constitute a closed hydraulic circuit. Thepump and motor distributor valves supply oil discharged from pumpplungers which are reciprocated in the pump cylinder by the revolutionof a pump swash plate to be driven into a motor cylinder chamber to pushmotor plungers so that they are moved in an axial direction in slidingcontact with a motor swash plate to drive the motor cylinder.

[0007] By changing the angle of the motor swash plate, the reciprocatingstrokes of the motor plungers, that is, the motor capacity is changedcontinuously to vary the revolution speed of the motor cylindercontinuously. When this speed change control is carried out, the angleof the motor swash plate is detected, and the control of the operationof a motor servo mechanism for controlling the angle of the motor swashplate is based on detection information on the angle of the motor swashplate. Therefore, the detection of the angle of the motor swash plate isnecessary. For example, JP-A 2001-343060 discloses that the rotationangle of a swash plate holder is detected by mounting a ratio detectionsensor, which is a potentiometer, to a casing.

[0008] The above known ratio detection sensor, that is, a swash plateangle detector is mounted to a transmission housing, and a revolutiondetection axis extending from this detector is secured to the swashplate holder (swash plate rolling member) to transmit the revolution ofthe swash plate holder turned by the tilting and rolling of the swashplate to the revolution detection axis as the tilting angle of the swashplate. However, as the swash plate angle detector is mounted to thecasing, the center of rolling of the swash plate rolling membersupported by the casing and the center of the revolution detection axisof the swash plate angle detector may slightly differ from each other.The revolution detection axis is mounted at an angle, accurate angledetection may not be carried out, and a detection error may occur.Therefore, it is necessary to prevent the above difference.

[0009] In other words, the swash plate angle detector must be mounted tothe casing such that the revolution detection axis of the swash plateangle detector becomes coaxial to the center of rolling of the swashplate rolling member. As a result, the installation position and theinstallation angle of the swash plate angle detector are limited,thereby reducing the degree of lay-out freedom. That is, to carry outthe optimum lay-out of the device, the installation of the swash plateangle detector must be taken into consideration for the lay-out and thedegree of lay-out freedom is low.

[0010] Although the known devices have utility for their intendedpurposes, there is still a need to provide an improved swash platetilting angle detector with greater lay-out freedom.

SUMMARY OF THE INVENTION

[0011] In view of the above disadvantage of known systems, it is anobject of the present invention to provide a swash plate tilting angledetector for a swash plate plunger type hydraulic unit, which caneliminate the conventional necessity of great control for securing thedetection accuracy of the swash plate angle detector and can make iteasy to control the installation position.

[0012] To attain the above object, according to the present invention,there is provided a swash plate plunger type hydraulic unit comprising acylinder which is rotatably supported and has a plurality of plungerholes extending in an axial direction and arranged in a loop to surrounda rotation axis thereof, a plurality of plungers slidably disposed inthe respective plunger holes, a swash plate (for example, motor swashplate 31 and motor rolling member 35 in the Embodiment disclosed below)to which the outer end portions of the plungers are contacted, and acasing supporting the swash plate in such a manner that it can tilt androll with a rolling axis perpendicular to the rotation axis as a center,and housing the swash plate and the cylinder. A swash plate tiltingangle detector detecting the tilting and rolling angle of the swashplate comprises an angle detector mounted to the casing and a rotationconnection mechanism having one end which is situated coaxial to therolling axis and connected to the swash plate and another end which isconnected to the angle detector, and the rotation connection mechanismaccurately transmits the rolling angle of the swash plate to the angledetector even when a rotation axis of a portion of the angle detectorconnected to the rotation connection mechanism is inclined at an anglewith respect to the rolling axis.

[0013] Preferably, the rotation connection mechanism comprises a firstconnection rod connected to the swash plate coaxially to the rollingaxis, a second connection rod connected to a rotation detector and amovable joint for connecting the first connection rod to the secondconnection rod.

[0014] According to the swash plate tilting angle detector for a swashplate plunger type hydraulic unit constituted as described above, theangle detector mounted to the casing and the swash plate are connectedto each other by the rotation connection mechanism (for example, therotation connection mechanism having a universal joint) which cantransmit the tilting and rolling angle of the rotation detection axisrelative to the angle detector accurately even when the rotationdetection axis of the angle detector is inclined at a predeterminedangle with respect to the axis of the swash plate. Therefore, even whenthe center of rolling of the swash plate and the center of the rotationdetection axis of the swash plate angle detector slightly differ fromeach other, the tilting and rolling angle of the swash plate istransmitted to the angle detector by the rotation connection mechanismaccurately to detect the accurate angle of the swash plate. Accordingly,the conventional necessity of great control for securing the detectionaccuracy of the swash plate angle detector is eliminated and it is easyto control the installation position of the detector.

[0015] For a more complete understanding of the present invention, thereader is referred to the following detailed description section, whichshould be read in conjunction with the accompanying drawings. Throughoutthe following detailed description and in the drawings, like numbersrefer to like parts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a sectional view of a hydraulic continuously variabletransmission having a swash plate tilting angle detector according to anillustrative embodiment of the present invention.

[0017]FIG. 2 is a side view of a rough or all terrain vehicle having theabove hydraulic continuously variable transmission according to anembodiment of the present invention.

[0018]FIG. 3 is a plan view of the rough terrain vehicle having theabove hydraulic continuously variable transmission according to anembodiment of the present invention.

[0019]FIG. 4 is a rear view of the rough terrain vehicle having theabove hydraulic continuously variable transmission according to anembodiment of the present invention.

[0020]FIG. 5 is a schematic diagram showing the power transmission lineof a power unit having the above hydraulic continuously variabletransmission according to an embodiment of the present invention.

[0021]FIG. 6 is a sectional view of part of the above hydrauliccontinuously variable transmission according to an embodiment of thepresent invention.

[0022]FIG. 7 is a sectional view of part of the above hydrauliccontinuously variable transmission according to an embodiment of thepresent invention.

[0023]FIG. 8 is an enlarged sectional view of part of the abovehydraulic continuously variable transmission according to an embodimentof the present invention.

[0024]FIG. 9 is a sectional view of a rotation connection mechanismconstituting the swash plate tilting angle detector in the hydrauliccontinuously variable transmission according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

[0025] One illustrative embodiment of the present invention will bedescribed hereinbelow with reference to the drawings. First, FIGS. 2 to4 show a rough or all terrain vehicle (RTV) which has a hydrauliccontinuously variable transmission provided with the swash plate tiltingangle detector of the present invention. This vehicle (RTV) incorporatesa power unit (PU) in a car body 80 having a frame structure therein andhas front wheels (FW) and rear wheels (RW) which are driven by theoutput of the power unit (PU). The car body 80 comprises a front fender81 situated at the front of the car body and provided with a front guard81 a, a saddle 82 which extends longitudinally and projects upward fromthe center of the car body, right and left steps 84 and 84 which extenddownward from the right and left sides of the saddle 82 in right andleft directions, and a rear fender 85 situated at the rear of the carbody and provided with a rear guard 85 a. The saddle 82 is provided witha seat 83 for a driver. The driver who strides over the saddle 82 to siton the seat 83 puts his/her feet on the right and left steps 84 andmanipulates a steering handle 86 which is situated in front of him/herand can be turned in right and left directions. A fuel tank (FT) isarranged in front of the saddle 82 as shown in FIG. 1.

[0026] The saddle 82 incorporates the power unit (PU) which comprises anengine (E), main clutch (CL), hydraulic continuously variabletransmission (CVT) and transmission gear train (GT) as will be describedhereinafter with reference to FIG. 5. The engine (E) takes in anair-fuel mixture prepared by mixing together air absorbed through an airfilter (AF) and fuel in the fuel tank (FT) in a carburetor (C) and bumsit in a cylinder to generate driving torque. An exhaust gas which isproduced after burning in the cylinder is discharged from an exhaustpipe (EP) through a muffler (M).

[0027] The driving torque of the engine (E) is transmitted from thecrank shaft to the main clutch (CL), hydraulic continuously variabletransmission (CVT) and transmission gear train (GT) while its speed ischanged and output to front and rear propeller shafts (FP, RP). Thefront propeller shaft (FP) is connected to a front differentialmechanism (FD) so that the driving torque output to the front propellershaft (FP) is transmitted from the front differential mechanism (FD) tothe right and left front wheels (FW) through right and left front axleshafts (FA) so as to drive the front wheels (FW). The rear propellershaft (RP) is connected to a rear differential mechanism (RD) so thatthe driving torque output to the rear propeller shaft (RP) istransmitted from the rear differential mechanism (RD) to the right andleft rear wheels (RW) through right and left rear axle shafts (RA) so asto drive the rear wheels (RW).

[0028] A description is subsequently given of the above power unit (PU)with reference to FIG. 5. The power unit (PU) comprises the engine (E)for generating driving torque, the main clutch (CL) for controlling thetransmission of the driving torque, the hydraulic continuously variabletransmission (CVT) for changing the driving torque transmitted throughthe main clutch (CL) continuously, and the transmission gear train (GT)for changing the direction of and transmitting the output revolution ofthe hydraulic continuously variable transmission (CVT). The power unit(PU) is incorporated in the saddle 82 in such a manner that the enginecrank shaft extends in the longitudinal direction of the car body.

[0029] The engine (E) is provided with a piston 2 in a cylinder 1 havingfeed and exhaust valves 1 a and 1 b in its head portion. In the engine(E), air absorbed through the air filter (AF) is mixed with fuel in thefuel tank (FT) in the carburetor (C) to prepare an air-fuel mixture asdescribed above, the air-fuel mixture is supplied into the cylinderchamber by opening the feed valve 1 a at a predetermined timing andburnt in the cylinder chamber to reciprocate the piston 2, thisreciprocation of the piston 2 is transmitted to a crank 3 a by aconnection rod 2 a, and a crank shaft 3 is turned. The main clutch (CL)is provided at the end of the crank shaft 3 to controlengagement/disengagement between an input drive gear 4 rotatablyinstalled on the crank shaft 3 and the crank shaft 3. Therefore, thedriving torque of the crank shaft 3 is transmitted to the input drivegear 4 in accordance with the control of engagement/disengagement by themain clutch (CL). The main clutch (CL) is composed of a centrifugalclutch, for example.

[0030] The hydraulic continuously variable transmission (CVT) has aswash plate plunger type hydraulic pump (P) and a swash plate plungertype hydraulic motor (M). An input slave gear 5 connected to a pumpcasing constituting the swash plate plunger type hydraulic pump (P)engages with the above input drive gear 4 so that the driving torque ofthe engine (E) is transmitted to the input slave gear 5 to turn the pumpcasing. The output revolution whose speed has been changed continuouslyby the hydraulic continuously variable transmission (CVT) to bedescribed in detail hereinafter is output to a transmission output shaft6.

[0031] The transmission output shaft 6 is connected to a transmissionoutput gear 11 constituting the above transmission gear train (GT) totransmit the revolution of the transmission output shaft 6 from thetransmission output gear 11 through the transmission gear train (GT).The transmission gear train (GT) has a counter shaft 15 and an idlershaft 13 arranged parallel to the transmission output shaft 6. Thecounter shaft 15 is fitted with a forward gear 12 and a backward gear 14in such a manner that they can turn freely, and connected to an outputdrive gear 17. Meanwhile, the idler shaft 13 is connected to a firstidler gear 13 a and a second idler gear 13 b. The forward gear 12engages with the transmission output gear 11, and the first idler gear13 a also engages with the transmission output gear 11. The second idlergear 13 b engages with the backward gear 14.

[0032] The forward gear 12 and the backward gear 14 are provided withinternal clutch gears 12 a and 14 a, respectively, and a clutch sleeve16 which can turn together with the counter shaft 15 to be moved in anaxial direction is provided between the forward gear 12 and the backwardgear 14. An external clutch gear 16 a is formed on the clutch sleeve 16to move the clutch sleeve 16 in the axial direction to be selectivelyengaged with the internal clutch gear 12 a or 14 a, thereby constitutinga dog clutch. This clutch sleeve 16 is moved in the axial direction bythe driver's manipulation of a shift lever to a forward movement side orbackward movement side.

[0033] When the driver moves the shift lever to the forward movementside, the clutch sleeve 16 is moved in the left direction in the figure,and the external clutch gear 16 a is engaged with the internal clutchgear 12 a to connect the forward gear 12 to the counter shaft 15.Therefore, in this state, the revolution of the transmission output gear11 is transmitted from the forward gear 12 to the counter shaft 15 toturn the output drive gear 17.

[0034] When the driver moves the shift lever to the backward movementside, the clutch sleeve 16 is moved in the right direction in thefigure, and the external clutch gear 16 a is engaged with the internalclutch gear 14 a to connect the backward gear 14 to the counter shaft15. In this state, the revolution of the transmission output gear 11 istransmitted from the first idler gear 13 a to the second idler gear 13 bthrough the idler shaft 13 and further from the second idler gear 13 bto the counter shaft 15 through the backward gear 14 engaged with thesecond idler gear 13 b to turn the output drive gear 17. The revolutiondirection of the output drive gear 17 at this point is the oppositedirection (backward direction) to the direction when the shift lever ismoved to the above forward movement side.

[0035] The output drive gear 17 engages with the output slave gear 18connected to a drive shaft 19 so that the revolution of the output drivegear 17 is transmitted to the drive shaft 19 through the output slavegear 18. The front end of the drive shaft 19 is linked to the frontpropeller shaft (FP) and the rear end of the drive shaft 19 is linked tothe rear propeller shaft (RP) so that the driving torque transmitted tothe drive shaft 19 is transmitted to the front and rear propeller shafts(FP, RP), whereby the front and rear wheels (FW, RW) are driven asdescribed above.

[0036] A description is subsequently given of the above hydrauliccontinuously variable transmission (CVT) with reference to FIG. 1 andFIGS. 6 to 8. The hydraulic continuously variable transmission (CVT) hasthe swash plate plunger type hydraulic pump (P) and the swash plateplunger type hydraulic motor (M), and the transmission output shaft 6extends through the hydraulic continuously variable transmission (CVT)passing the center thereof. The transmission output shaft 6 is supportedin a transmission housing (HSG) such that it can turn by ball bearings 7a and 7 b.

[0037] The hydraulic pump (P) comprises a pump casing 20 which ismounted to the transmission output shaft 6 in such a manner that it iscoaxial to and rotated relative to the transmission output shaft 6, apump swash plate member 21 which is installed in the pump casing 20 andinclined at a predetermined angle from the rotation axis of the pumpcasing 20, a pump cylinder 22 which is opposed to the pump swash platemember 21, and a plurality of pump plungers 23 which are slidably laidin a plurality of pump plunger holes 22 a formed in the axial directionand arranged in a loop surrounding the center axis of the pump cylinder22. The pump casing 20 is supported on the transmission output shaft 6such that it can turn by a bearing 8 a and also supported in thetransmission housing (HSG) such that it can turn by a bearing 8 b. Thepump swash plate member 21 is installed in the pump casing 20 in such amanner that it can turn on an axis inclined at the above predeterminedangle by bearings 21 a and 21 b. The pump cylinder 22 is supported inthe pump casing 20 in such a manner that it can turn by a bearing 22 crelative to and coaxial to the pump casing 20.

[0038] The input slave gear 5 is fitted onto the pump casing 20 byfastening a bolt Sa. The outer end portion of each of the pump plungers23 projects outward and is contacted to and engaged with the swash plateface 21 a of the pump swash plate member 21, and the inner end portionsituated in the pump plunger hole 22 a is opposed to the valve body 51of a distributor valve 50 (which will be described hereinafter) to forma pump oil chamber 23 a in the pump plunger hole 22 a. A pump opening 22b which serves as the outlet and inlet of the pump is formed at the endof the pump plunger hole 22 a. When the input slave gear 5 is turned,the pump casing 20 is turned as described above, the pump swash platemember 21 situated in the pump casing 20 is moved by the rotation of thepump casing 20, and the pump plungers 23 are reciprocated in the pumpplunger holes 22 a by the movement of the swash plate faces 21 a tocompress or expand hydraulic oil in the pump oil chambers 23 a.

[0039] The hydraulic motor M comprises a motor casing 30 which isconnected to the transmission housing (HSG) to be fixed and held, amotor rolling member 35 which is in sliding contact with a supportspherical face 30 a formed on the inner wall of the motor casing 30 andsupported such that it can turn with the center O extending in adirection (vertical direction to the sheet of the figure) perpendicularto the center axis of the transmission output shaft 6 as the center, amotor swash plate member 31 supported in the motor rolling member 35such that it can turn by bearings 31 a and 31 b, a motor cylinder 32opposed to the motor swash plate member 31, and a plurality of motorplungers 33 which are slidably laid in a plurality of motor plungerholes 32 a formed in the axial direction and arranged in a loopsurrounding the center axis of the motor cylinder 32. The motor cylinder32 is supported in the motor casing 30 by a bearing 32 c such that itcan turn.

[0040] The outer end portion of each of the motor plungers 33 projectsoutward and is contacted to and engaged with the swash plate face 31 aof the motor swash plate member 31, and the inner end portion situatedin the plunger hole 32 a is opposed to the valve body 51 to form a motoroil chamber 33 a in the motor plunger hole 32 a. A motor opening 32 bwhich serves as the outlet and inlet of the motor is formed at the endof the motor plunger hole 32 a. An arm portion 35 a which projectsoutward from the end of the motor rolling member 35 in the radialdirection is connected to a motor servo mechanism (SV) which controlsthe horizontal movement in the figure of the arm portion 35 a to carryout the control of the revolution on the center O of the motor rollingmember 35. When the motor rolling member 35 is turned, the motor swashplate member 31 which is rotatably supported in the motor rolling member35 is also turned and the angle of its swash plate is changed.

[0041] The distributor valve 50 is provided between the pump cylinder 22and the motor cylinder 32. The valve body 51 of the distributor valve 50is sandwiched between and integrally connected to the pump cylinder 22and the motor cylinder 32 and also connected to the transmission outputshaft 6. Therefore, the pump cylinder 22, distributor valve 50, motorcylinder 32 and transmission output shaft 6 turn together.

[0042] To show reference symbols clearly in FIG. 7 in particular, aplurality of pump-side spool holes 51 a and a plurality of motor-sidespool holes 51 b extending in the radial direction are formed in tworows in the valve body 51 constituting the distributor valve 50 at equalintervals in the circumferential direction. Pump-side spools 53 areslidably laid in the pump-side spool holes 51 a, and motor-side spools55 are slidably laid in the motor-side spool holes 51 b.

[0043] The pump-side spool holes 51 a are formed corresponding to thepump plunger holes 22 a, and a plurality of pump-side communicationpaths 51 c communicating with the respective pump openings 22 b (pumpoil chambers 23 a) and the respective pump-side spool holes 51 a areformed in the valve body 51. The motor-side spool holes 51 b are formedcorresponding to the motor plunger holes 32 a, and a plurality ofmotor-side communication paths 51 d communicating with the respectivemotor openings 32 b (motor oil chambers 33 a) and the respectivemotor-side spool holes 51 b are formed in the valve body 51 (see FIG.1).

[0044] In the distributor valve 50, a pump-side cam ring 52 is disposedat a position surrounding the outer ends of the pump-side spools 53, anda motor-side cam ring 54 is disposed at a position surrounding the outerends of the motor-side spools 55. The pump-side cam ring 52 is mountedon the eccentric inner face 20 a formed eccentric to the center axis ofthe rotation of the pump casing 20 on the inner wall at the end of thepump casing 20 so that it is turned together with the pump casing 20.The motor-side cam ring 54 is mounted on the eccentric inner face 30 aformed eccentric to the center axis of the rotation of the motorcylinder 32 on the inner wall at the end of the motor casing 30. Theouter ends of the pump-side spools 53 are secured to the inner wall ofthe pump-side cam ring 52 in such a manner that they can turn relativeto the pump-side cam ring 52, and the outer ends of the motor-sidespools 55 are secured to the inner wall of the motor-side cam ring 54 insuch a manner that they can turn relative to the motor-side cam ring 54.

[0045] An inner path 56 is formed between the inner wall of the valvebody 51 and the outer wall of the transmission output shaft 6, and theinner ends of the pump-side spool holes 51 and the motor-side spoolholes 51 b communicate with this inner path 56. An outer path 57 whichcommunicates with the pump-side spool holes 51 a and the motor-sidespool holes 51 b is formed in the valve body 51.

[0046] A description is subsequently given of the operation of the aboveconstituted distributor valve 50. When the drive force of the engine (E)is transmitted to the input slave gear 5 to turn the pump casing 20, thepump swash plate member 21 is rolled by this revolution. Therefore, thepump plungers 23 which are contacted to and engaged with the swash platefaces 21 a of the pump swash plate member 21 are reciprocated in theaxial direction in the respective pump plunger holes 22 a by the rollingof the pump swash plate member 21, and hydraulic oil is discharged fromthe pump oil chambers 23 a through the pump openings 22 b by the inwardmovements of the pump plungers 23 and absorbed into the pump chambers 23a through the pump openings 22 b by the outward movements of the pumpplungers 23.

[0047] Although the pump-side cam ring 52 mounted to the end of the pumpcasing 20 is turned together with the pump casing 20, the pump-sidespools 53 are reciprocated in the radial direction in the respectivepump-side spool holes 51 a by the revolution of the pump-side cam ring52 as it is mounted eccentric to the rotation center of the pump casing20. When the pump-side spools 53 are thus reciprocated and moved totheir inner-diameter side as shown in the upper half part of FIG. 1, thepump-side communication paths 51 c and the outer path 57 communicatewith each other through spool grooves 53 a and when the pump-side spools53 are moved to their outer-diameter side as shown in the lower halfpart of FIG. 1, the pump-side communication paths 51 c and the innerpath 56 communicate with each other through the spool grooves 53 a.

[0048] When the swash plate member 21 is rolled by the revolution of thepump casing 20 to reciprocate the pump plungers 23, the position ofeccentricity is set such that the pump-side cam ring 52 moves thepump-side spools 53 to their inner-diameter side during the half roundof the pump casing 20 during which the pump plungers 23 are moved from aposition where they are pushed the most outward (to be referred to as“lower dead center”) to a position where they are pushed the most inward(to be referred to as “upper dead center”) and to their outer-diameterside during the half round of the pump casing 20 during which the pumpplungers 23 are moved from the upper dead center to the lower deadcenter.

[0049] As a result, when the pump plungers 23 are moved from the lowerdead center to the upper dead center by the revolution of the pumpcasing 20 to discharge the hydraulic oil in the pump oil chambers 23 afrom the pump openings 22 b, this hydraulic oil is supplied into theouter path 57 through the pump-side communication paths 51 c. When thepump plungers 23 are moved from the upper dead center to the lower deadcenter by the revolution of the pump casing 20, the hydraulic oil in theinner path 56 is absorbed into the pump oil chambers 23 a through thepump-side communication paths 51 c and the pump openings 22 b. Asunderstood from this, when the pump casing 20 is turned, the hydraulicoil discharged from the hydraulic pump (P) is supplied into the outerpath 57 where it is supplied to the hydraulic motor (M), and hydraulicoil is absorbed into the hydraulic pump (P) from the inner path 56.

[0050] Since the motor-side cam ring 54 attached to the end of the motorcasing 30 is also mounted eccentric to the rotation center of the motorcasing 30, when the motor cylinder 32 is turned, the motor-side spools55 are reciprocated in the radial direction in the respective motor-sidespool holes 51 b by the revolution of the motor cylinder 32. When themotor-side spools 55 are thus reciprocated and moved to theirinner-diameter side as shown in the upper half part of FIG. 1, themotor-side communication paths 51 d and the outer path 57 communicatewith each other through the spool grooves 55 a and when the motor-sidespools 55 are moved to their outer-diameter side as shown in the lowerhalf part of FIG. 1, the motor-side communication paths 51 d and theinner path 56 communicate with each other through the spool grooves 55a.

[0051] The hydraulic oil discharged from the hydraulic pump (P) issupplied into the outer path 57 as described above and further the motoroil chambers 33 a from the motor-side communication paths 51 d throughthe motor openings 32 b, and the motor plungers 33 are pushed outward inthe axial direction. The outer ends of the motor plungers 33 whichreceive outward pressure in the axial direction are slidably contactedto a portion from the upper dead center to the lower dead center of themotor swash plate member 31 while the motor rolling member 35 is rolledas shown in FIG. 1. The motor cylinder 32 is turned so that the motorplungers 33 are moved from the upper dead center to the lower deadcenter along with the motor swash plate member 31 by this outwardpressure in the axial direction.

[0052] To carry out this revolution, the position of eccentricity of themotor-side cam ring 54 is set such that when the motor plungers 33 arereciprocated along with the inclination of the motor swash plate member31 by the revolution of the motor cylinder 32, the motor-side cam ring54 moves the motor-side spools 55 to their outer-diameter side duringthe half round of the motor cylinder 32 during which the motor plungers33 are moved from a position (lower dead center) where they are pushedthe most outward to a position where they are pushed the most inward(upper dead center) and to their outer-diameter side during the halfround of the motor cylinder 32 during which the motor plungers 33 aremoved from the upper dead center to the lower dead center.

[0053] When the motor cylinder 32 is thus turned, the motor plungers 33are pushed inward while they are moved from the lower dead center to theupper dead center along with the motor swash plate member 31 by thisrevolution, and hydraulic oil in the motor oil chambers 33 a is suppliedinto the inner path 56 from the motor openings 32 b through themotor-side communication paths 51 d. Thus, hydraulic oil supplied intothe inner path 56 is absorbed into the pump oil chambers 23 a throughthe pump-side communication paths 51 c and the pump openings 22 b asdescribed above.

[0054] As understood from the above description, when the pump casing 20is turned by the driving torque of the engine (E), hydraulic oil isdischarged into the outer path 57 from the hydraulic pump (P) andsupplied into the hydraulic motor (M) to turn the motor cylinder 32. Thehydraulic oil which has turned the motor cylinder 32 is supplied intothe inner path 56 and absorbed into the hydraulic pump (P) from theinner path 56. Thus, a closed hydraulic circuit for connecting thehydraulic pump (P) to the hydraulic motor (M) is composed of thedistributor valve 50. Specifically, the hydraulic oil discharged fromthe hydraulic pump (P) by the revolution of the hydraulic pump (P) issupplied into the hydraulic motor (M) through the closed hydrauliccircuit to drive the hydraulic motor (M), and the hydraulic oildischarged by driving the hydraulic motor (M) is returned to thehydraulic pump (P) through the closed hydraulic circuit.

[0055] Since the pump cylinder 22 and the motor cylinder 32 areconnected to the transmission output shaft 6 and turned together, whenthe motor cylinder 32 is turned as described above, the pump cylinder 22is also turned and the revolution speed of the pump casing 20 relativeto the pump cylinder 22 becomes low. Therefore, the relationship betweenthe revolution speed Ni of the pump casing 20 and the revolution speedNo of the transmission output shaft 6 (that is, the revolution speeds ofthe pump cylinder 22 and the motor cylinder 32) is expressed by thefollowing equation (1) based on the capacity Vp of the pump and thecapacity (Vm) of the motor.

[0056] Equation 1

Vp(Ni-No)=VmNo  (1)

[0057] The capacity Vm of the motor can be changed continuously bycontrol for rolling the motor rolling member 35 by means of the motorservo mechanism (SV). Therefore, when the revolution speed Ni of thepump swash plate member 21 is fixed in the above equation (1) and themotor capacity Vm is changed continuously, the control of speed changefor changing the revolution of the transmission output shaft 6 iscontinuously carried out.

[0058] When control for reducing the rolling angle of the motor rollingmember 35 is carried out, the motor capacity Vm becomes small and whenthe pump capacity Vp is fixed in the relationship of the above equation(1) and the revolution speed Ni of the pump swash plate member 21 isfixed, control is made to increase the revolution of the transmissionoutput shaft 6 to the revolution speed Ni of the pump swash plate member21, that is, to change it to the top gear continuously. When the angleof the motor swash plate becomes null, that is, 90°, the change gearratio (top gear ratio) becomes Ni=No theoretically and the hydrauliclocked state is obtained. As a result, the pump casing 20 is turnedtogether with the pump cylinder 22, the motor cylinder 32 and thetransmission output shaft 6 to supply mechanical power.

[0059] Control for changing the motor capacity continuously is carriedout by changing the angle of the motor swash plate by rolling the motorrolling member 35. The motor servo mechanism (SV) for rolling the motorrolling member 35 will be described hereinbelow with reference to FIG. 6mainly.

[0060] The motor servo mechanism (SV) comprises a ball screw shaft 61which is situated in the vicinity of the arm portion 35 a of the motorrolling member 35, extends parallel to the transmission output shaft 6and is supported in the transmission housing (HSG) such that it can turnby bearings 60 a and 60 b, and a ball nut 62 which is mated with a malescrew 61 a formed on the outer wall of the ball screw shaft 61. A ballthread 62 a is formed by a plurality of balls which are held on theinner wall of the ball nut 62 by a cage and arranged in a screw form andmated with the male screw 61 a. The ball nut 62 is connected to the armportion 35 a of the motor rolling member 35 and moved in a horizontaldirection over the ball screw shaft 61 such that the motor rollingmember 35 is rolled when the ball screw shaft 61 is turned.

[0061] To drive the ball screw shaft 61 as described above, a swashplate control motor (electric motor) 67 is attached to the outer endface of the transmission housing (HSG). The drive shaft 67 a of theswash plate control motor 67 is connected to a spacer shaft 65 by acoupling 66. This spacer shaft 65 extends beyond the periphery of theinput slave gear 5 close to the end portion of the above ball screwshaft 61 and parallel to the transmission output shaft 6 in thetransmission housing (HSG) and is rotatably supported in thetransmission housing (HSG). An idle shaft 64 c which extends parallel tothe spacer shaft 65 is supported in the transmission housing (HSG), andan idle gear member 64 is rotatably mounted on this idle shaft 64 c.

[0062] A first gear 65 a is formed at the end of the spacer shaft 65 andengages with a second gear 64 b formed integrated with the idle gearmember 64. A third gear 64 a formed integrated with the idle gear member64 engages with a fourth gear 63 which is fitted onto the end of theabove ball screw shaft 61. Therefore, when the drive shaft 67 a isturned by controlling the revolution of the swash plate control motor67, this revolution is transmitted to the fourth gear member 63 throughthe idle gear member 64 to turn the ball screw shaft 61, and the ballnut 62 is moved in the horizontal direction over the shaft 61 to rollthe motor rolling member 35.

[0063] When control is made to roll the motor rolling member 35, theactual titling and rolling angle of the motor rolling member 35 isaccurately detected and the drive control of the swash plate controlmotor 67 is carried out based on detection information on the tiltingand rolling angle. Therefore, it is important that the actual tiltingand rolling angle of the motor rolling member 35 should be detectedaccurately, and the swash plate tilting angle detector for detectingthis angle will be described with reference to FIG. 8.

[0064]FIG. 8 is a sectional view of a hydraulic continuously variabletransmission (CVT) cut on a plane passing through the center axis O ofrolling of the motor rolling member 35 and the center axis of rotationof the transmission output shaft 6. A shaft securing member 36 is fixedto a portion passing through the center axis of rolling at the side endof the motor rolling member 35. An angle detector 37, which is apotentiometer, is mounted to the transmission housing (HSG) and has anelectric connector 37 a for obtaining a detection signal. A rotationconnection mechanism 40 is arranged to connect the shaft securing member36 to the angle detector 37 (detection axis of the detector).

[0065] This rotation connection mechanism 40 is shown in FIG. 9 andcomprises a first connection rod 41 having an engagement portion 41 a tobe engaged with the shaft securing member 36 and a second connection rod42 having an engaging portion 42 a to be engaged with the angle detector37 both of which are connected by a pin 43 in such a manner that theycan move as shown in FIG. 9. This pin 43 is somewhat loosely connectedor fitted so that the second connection rod 42 can move or pivotrelative to the first connection rod 41 at an angle. A universal jointmechanism such as a spherical joint may be used in place of the pin 43.Further, a flexible rod or a shaft member (such as a rubber tube) may beused as the rotation connection mechanism. Particularly when therotation connection mechanism is a universal joint, if the secondconnection rod 42 is greatly inclined with respect to the firstconnection rod 41, revolution will still be transmitted and detectedaccurately. Therefore, when the angle detector 37 is to be mounted tothe casing, the restriction of its installation position and angle issmall and the degree of lay-out freedom is high.

[0066] The first connection rod 41 of the rotation connection mechanism40 is engaged with the shaft securing member 36 and turned by therolling of the motor rolling member 35, the second connection rod 42 isconnected to the first connection rod 41 by the pin 43 to be turnedtogether with the first connection rod 41 so as to transmit thisrevolution to the angle detector 37, whereby the rolling angle of themotor rolling member 35, that is, the swash plate angle of the motorswash plate 31 is detected. Since the inclination of the secondconnection rod 42 with respect to the first connection rod 41 to acertain degree is allowed, even when the center of the detection axis ofthe angle detector 37 mounted to the transmission housing (HSG) isslightly inclined with respect to the center axis O of tilting androlling of the motor rolling member 35, the tilting and rolling of themotor rolling member 35 are transmitted to the angle detector 37accurately and smoothly, thereby making it possible to accurately detectthe tilting and rolling angle (the angle of the swash plate). Since theinstallation position accuracy of the angle detector 37 may be slightlylow, the degree of lay-out freedom of the angle detector 37 is high.

[0067] When oil flows through the closed hydraulic circuit to transmithydraulic force between the hydraulic pump (P) and the hydraulic motor(M) as described above, oil leakage from the hydraulic closing circuitand oil leakage from mating portions between the pump and the motorplunger holes 22 a and 32 a and mating portions between the pump and themotor plungers 23 and 33 occur. Therefore, a charge oil supply hole 6 aextending in the axial direction is formed in the transmission outputshaft 6 and connected to a first check valve (CV1) mounted in the pumpcylinder 22 through an oil path 6 b formed in the transmission outputshaft 6 and an oil path 51 e formed in the pump cylinder 22 and furtherto the inner path 56 from the first check valve (CV1) through an oilpath 51 f as shown in FIG. 7. Therefore, charge oil supplied from anunshown charge oil supply source to the charge oil supply hole 6 a issupplied into the inner path 56 through the first check valve (CV1) asrequired.

[0068] The charge oil supply hole 6 a is connected to a second checkvalve (CV2) mounted in the pump cylinder 22 through an oil path 6 cformed in the transmission output shaft 6 and an oil path 51 g formed inthe pump cylinder 22 and further to the outer path 57 from the secondcheck valve (CV2) through an oil path 51 h. Therefore, the charge oilsupplied into the charge oil supply hole 6 a is supplied into the outerpath 57 through the second check valve (CV2) as required.

[0069] As understood from the description of the operations of thehydraulic pump (P) and the hydraulic motor (M), when the hydraulic motor(M) is in a normal running state, that is, is driven with hydraulic oilfrom the hydraulic pump (P), the inside pressure of the outer path 57 ishigh and the inside pressure of the inner path 56 is low, whereby thecharge oil is supplied into the innerpath 56 through the first checkvalve (CV1). However, when the vehicle is running by using engine brake,the inside pressure of the outer path 57 is low and the inside pressureof the inner path 56 is high, whereby charge oil is supplied into theouter path 57 through the second check valve (CV2).

[0070] As shown in FIG. 8, first and second relief valves (RV1, RV2) areinstalled in the pump cylinder 22. The first relief valve (RV) connectsthe outer path 57 to the inner path 56. When the pressure of oil in theouter path 57 becomes a predetermined level or higher, the first reliefvalve is opened to discharge oil into the inner path 56, therebypreventing the pressure of oil in the outer path 57 from becoming toohigh. The second relief valve (RV2) connects the inner path 56 to theouter path 57. When the pressure of oil in the inner path 56 becomes apredetermined level or higher, the second relief valve (RV2) is openedto discharge oil into the outer path 57, thereby preventing the pressureof oil in the inner path 56 from becoming too high.

[0071] As described above, according to the present invention, the swashplate tilting angle detector for detecting the tilting and rolling angleof the swash plate comprises an angle detector mounted to a casing and arotation connection mechanism which has one end situated coaxial to thetitling and rolling axis and connected to the swash plate and the otherend connected to the angle detector. The rotation connection mechanismis constituted (for example, comprising a first connection rod connectedto the swash plate coaxially to the tilting and rolling axis, a secondconnection rod connected to a rotation detector, and a movable joint forconnecting the first connection rod to the second connection rod) suchthat it can transmit the tilting and rolling angle of the swash plate tothe angle detector accurately even when the rotation axis of a portionconnected to the rotation connection mechanism of the angle detector isinclined at a predetermined angle with respect to the tilting androlling axis. Therefore, even when the rolling center of the swash plateand the center of the rotation detection axis of the swash plate angledetector slightly differ from each other, the tilting and rolling angleof the swash plate can be transmitted to the angle detector by therotation connection mechanism accurately to enable the accuratedetection of the angle of the swash plate. Consequently, theconventional necessity of great control for securing the detectionaccuracy of the swash plate angle detector is eliminated, and it becomeseasy to control the detector's installation position.

[0072] Although the present invention has been described herein withrespect to a specific illustrative embodiment thereof, the foregoingdescription is intended to be illustrative, and not restrictive. Thoseskilled in the art will realize that many modifications of theembodiment could be made which would be operable. All such modificationswhich are within the scope of the claims are intended to be within thescope and spirit of the present invention.

Having thus, described the invention, what is claimed is:
 1. A swashplate plunger type hydraulic unit comprising: a cylinder which isrotatably supported and has a plurality of plunger holes extending in anaxial direction and arranged in a loop to surround a rotation axisthereof; plurality of plungers slidably disposed in the respectiveplunger holes; swash plate to which outer end portions of the plungersare contacted; casing for supporting the swash plate in such a mannerthat it can tilt and roll with a rolling axis perpendicular to therotation axis as a center, and housing the swash plate and the cylinder;and swash plate tilting angle detector detecting a tilting and rollingangle of the swash plate; the swash plate tilting angle detectorcomprising an angle detector mounted to the casing and a rotationconnection mechanism having one end which is situated coaxial to therolling axis and connected to the swash plate and another end which isconnected to the angle detector; and the rotation connection mechanismaccurately transmits the tilting and rolling angle of the swash plate tothe angle detector even when a rotation axis of a portion of the angledetector connected to the rotation connection mechanism is inclined atan angle with respect to the rolling axis.
 2. A swash plate typehydraulic unit of claim 1, wherein the rotation connection mechanismcomprises a first connection rod which is connected to the swash platecoaxially to the rolling axis, a second connection rod connected to therotation detector, and a movable joint connecting the first connectionrod to the second connection rod.
 3. A swash plate type hydraulic unitof claim 2, wherein the movable joint comprises a pin.
 4. A swash platetype hydraulic unit of claim 2, wherein the movable joint comprises oneof a universal joint and a pin.
 5. A swash plate type hydraulic unit ofclaim 1, wherein the one end of the rotation connection mechanism isconnected to the swash plate through a shaft securing member.
 6. A swashplate type hydraulic unit of claim 1, further comprising a rollingmember connected to the swash plate and through which the swash platecan tilt and roll with the rolling axis.
 7. A swash plate type hydraulicunit of claim 6, wherein the one end of the rotation connectionmechanism is connected to the rolling member.
 8. A swash plate plungertype hydraulic unit comprising: a cylinder which is rotatably supportedand has a plurality of plunger holes extending in an axial direction andarranged in a loop to surround a rotation axis thereof; a plurality ofplungers slidably disposed in the respective plunger holes; a swashplate to which outer end portions of the plungers are contacted; acasing for supporting the swash plate in such a manner that it can tiltand roll with a rolling axis perpendicular to the rotation axis as acenter, and housing the swash plate and the cylinder; and a swash platetilting angle detector detecting a tilting and rolling angle of theswash plate; the swash plate tilting angle detector comprising an angledetector mounted to the casing and a rotation connection mechanismhaving one end which is situated coaxial to the rolling axis andconnected to the swash plate and another end which is connected to theangle detector; and the rotation connection mechanism includes a firstconnection rod which is fixed to the swash plate coaxially to therolling axis, and a second connection rod fixed to the rotation detectorand movably connected to the first connection rod.
 9. A swash plate typehydraulic unit of claim 8, wherein the first and second connection rodsare movably connected such that the rotation connection mechanismaccurately transmits the tilting and rolling angle of the swash plate tothe angle detector even when a rotation axis of a portion of the angledetector connected to the rotation connection mechanism is inclined atan angle with respect to the rolling axis.
 10. A swash plate typehydraulic unit of claim 8, wherein the first and second connection rodsare movably connected through one of a universal joint and a pin.
 11. Aswash plate type hydraulic unit of claim 8, wherein the one end of therotation connection mechanism is connected to the swash plate through ashaft securing member.
 12. A swash plate type hydraulic unit of claim 8,further comprising a rolling member connected to the swash plate andthrough which the swash plate can tilt and roll with the rolling axis.13. A swash plate type hydraulic unit of claim 12, wherein the one endof the rotation connection mechanism is connected to the rolling member.